The present invention relates to an exercise load intensity evaluation device which evaluates the exercise load intensity of a subject, and to exercise equipment. More particularly, the present invention relates to an exercise load intensity evaluation device capable of evaluating whether or not current exercise load intensity is safe and effective or of evaluating the exercise load intensity, and to exercise equipment.
It is known in the art that an anaerobic threshold (AT), which represents a threshold value at which the lactate concentration in blood starts to increase (also called a threshold value at which aerobic exercise is shifted to anaerobic exercise) as exercise load intensity or oxygen intake, is an index useful for evaluating the effect of exercise on the function of the respiratory system or the circulatory system, or for selecting suitable exercise load intensity in sport training. The anaerobic threshold may be detected by detecting a lactate threshold (LT) which is exercise load intensity or oxygen intake at which the lactate concentration in blood suddenly starts to increase, or detecting a ventilatory threshold (VT) which is exercise load intensity or oxygen intake at which the rate of increase in carbon dioxide in expired air accompanied by an increase in exercise load intensity significantly increases. The anaerobic threshold approximates a catecholamine threshold (CT) at which sympathetic nervous activities are accelerated. waveform, an electrocardiophonograph, or a pulse waveform measured noninvasively. The ejection duration measurement section may include an ejection duration correction section which corrects the cardiac ejection duration based on output from a pulse waveform detection section.
The cardiac ejection duration is constant or decreases to only a small extent even if the exercise load intensity increases. However, the ejection duration significantly decreases after the exercise load intensity exceeds the lactate threshold (LT), and a definite inflection point is recognized near the lactate threshold. Therefore, if a change in the ejection duration is detected by using the ejection duration change detection section when the subject is exercising while increasing the exercise load intensity, it is possible to evaluate whether the current exercise load intensity has or has not reached the lactate threshold. For example, exercise at exercise load intensity near the lactate threshold may be defined as safe and effective exercise as an index. This exercise load intensity range may be determined based on output from the ejection duration change detection section. The exercise load intensity evaluation device of the present invention may notify the subject of this exercise load intensity by using the heart rate and power (watt).
An exercise load intensity evaluation device according to another aspect of the present invention comprises:
a diastolic time measurement section which noninvasively measures cardiac diastolic time of a subject during exercise; and
a diastolic time change detection section which detects a change in the diastolic time which is measured at each measurement time by the diastolic time measurement section and is input to the diastolic time change detection section.
The diastolic time (DT) is time equivalent to a cardiac diastolic phase, and may be estimated from a feature of an electrocardiogram waveform or a pulse waveform measured noninvasively.
The cardiac diastolic time decreases as the exercise load intensity increases. However, the diastolic time is constant or changes to only a small extent after the exercise load intensity exceeds the lactate threshold (LT), and a definite inflection point is recognized near the lactate threshold. Therefore, if a change in the diastolic time is detected by using the diastolic time change detection section when the subject is exercising while increasing the exercise load intensity, it is possible to evaluate whether the current exercise load intensity has or has not reached the lactate threshold. Therefore, exercise at exercise load intensity near the lactate threshold may be defined as safe and effective exercise as an index in the same manner as in the case of the ejection duration, and this exercise load intensity range may be determined based on output from the diastolic time change detection section. The exercise load intensity evaluation device may notify the subject of this exercise load intensity by using the heart rate and power (watt).
A configuration substantially the same for the ejection duration and the diastolic time is described below.
The exercise load intensity evaluation device may further comprise an exercise load intensity measurement section which measures exercise load intensity of the subject. In this case, the ejection duration (diastolic time) change detection section may detect a change in the ejection duration (diastolic time) corresponding to different degrees of exercise load intensity based on output from the exercise load intensity measurement section. Therefore, if the ejection duration corresponding to different degrees of exercise load intensity substantially differs, or if the diastolic time corresponding to different degrees of exercise load intensity is substantially the same, the exercise may be recognized as exercise at exercise load intensity exceeding the lactate threshold.
In the exercise load intensity evaluation device of this aspect, the ejection duration (diastolic time) measurement section may further include: a body movement waveform detection section which detects a body movement waveform according to body movement of the subject during exercise; and a body movement waveform removal section which removes the body movement waveform detected by the body movement waveform detection section from the pulse wave detected by the pulse wave detection section. Since the body movement during exercise adversely influences the pulse wave, it is preferable to remove the influence of body movement. In this case, since the pulse wave from which the body movement waveform has been removed is input to the ejection duration (diastolic time) measurement section, the exercise load intensity can be evaluated with higher accuracy.
The ejection duration measurement section may measure a time interval from rise of the pulse wave to a dicrotic notch. The time interval from the rise of the pulse wave to the dicrotic notch reflects the ejection duration as described later in detail.
The diastolic time measurement section may measure the diastolic time by subtracting ejection duration from rise of the pulse wave to a dicrotic notch from one cycle of the pulse wave. The time interval from the rise of the pulse wave to the dicrotic notch reflects the ejection duration, and the sum of the ejection duration and the diastolic time equals one cycle of the pulse wave as described later in detail.
The cardiac ejection duration may be calculated from an electrocardiophonograph. Therefore, a time interval from rise of the pulse wave to the dicrotic notch may be corrected as the ejection duration from a correlation equation between systolic time obtained by measuring in advance a time interval from an aortic valve opening time S1 to an aortic valve closing time S2 by using the electrocardiophonograph and the time interval from rise of the pulse wave to the dicrotic notch.
The ejection duration (diastolic time) measurement section may include a first differentiation section which differentiates the pulse wave; and a second differentiation section which differentiates the pulse wave differentiated by the first differentiation section. Since the feature of the pulse wave described above becomes more obvious in the pulse waves differentiated by the first and the second differentiation sections, the ejection duration (diastolic time) can be measured based on these differentiated pulse waves.
The ejection duration (diastolic time) measurement section may include a comparator which compares a wave height of the pulse wave with a reference value. The ejection duration may be measured based on a pulse width of a rectangular wave output from the comparator. The diastolic time may be calculated by subtracting the ejection duration from one cycle of the pulse wave. In this case, a comparator with hysteresis and having a positive input terminal which is connected with a feed back resistor may be used. The comparator with hysteresis is capable of delaying rise of the rectangular wave even if the wave height of the pulse wave exceeds the reference value immediately after the rectangular wave falls near the dicrotic notch, for example. This enables a rectangular wave which reflects the ejection duration to be generated.
The ejection duration (diastolic time) measurement section may include a Fourier transformation section which transforms the pulse wave detected by the pulse wave detection section. In this case, the ejection duration (diastolic time) measurement section may extract a frequency spectrum which is obtained based on the feature of the pulse wave which reflects the cardiac ejection duration (diastolic time) from Fourier transformed frequency spectra. The ejection duration (diastolic time) change detection section may detect a change in frequency of the frequency spectrum extracted at each measurement time by the ejection duration (diastolic time) measurement section. This enables the change in the ejection duration (diastolic time) to be detected based on the frequency spectrum.
The ejection duration (diastolic time) measurement section may further includes: a first Fourier transformation section which transforms the pulse wave detected by the pulse wave detection section; and a second Fourier transformation section which transforms the body movement waveform detected by the body movement waveform detection section. In this case, the body movement waveform removal section may subtract frequency spectra at the same frequency among frequency spectra in each frequency band output from the first and second Fourier transformation sections. This enables the body movement to be removed at the stage of the frequency spectrum. The subsequent detection of the ejection duration (diastolic time) and the change in the ejection duration (diastolic time) may be performed based on the frequency spectrum in the same manner as described above.
The ejection duration (diastolic time) measurement section may include an inverse Fourier transformation section which performs inverse Fourier transformation of output from the body movement waveform removal section, and measure a time interval from rise of the inverse Fourier transformed pulse wave to a dicrotic notch. The ejection duration (diastolic time) measurement section may include a first differentiation section which differentiates the pulse wave which has been inverse-Fourier-transformed; and a second differentiation section which differentiates the pulse wave differentiated by the first differentiation section, and measures the ejection duration (diastolic time) based on the pulse wave differentiated by the first or second differentiation section.
The exercise load intensity evaluation device of the present invention may further comprise a notification section which notifies the subject that the exercise is anaerobic exercise at an exercise load intensity exceeding the lactate threshold based on output from the ejection duration (diastolic time) change detection section. This enables the subject to continue exercising at exercise load intensity near the lactate threshold. It suffices that the subject maintain the exercise load intensity constant when notified from the notification section.
The notification section may notify the subject of a heart rate calculated from one cycle of the heartbeat output from the ejection duration (diastolic time) change detection section.
An exercise load intensity evaluation device according to another aspect of the present invention comprises an exercise load intensity detection section which detects exercise load intensity from a storage section based on the ejection duration (diastolic time) measured by the ejection duration (diastolic time) measurement section instead of, or in addition to, the ejection duration (diastolic time) change detection section. The correlation data between the cardiac ejection duration (diastolic time) and the exercise load intensity of the subject is stored in advance in the storage section. This enables the exercise load intensity to be recognized during exercise.
The exercise load intensity detection section may detect the exercise load intensity when the ejection duration (diastolic time) change detection section detects that the ejection duration (diastolic time) is changed.
In the present invention, a ratio of the ejection duration (diastolic time) to one cycle of a heartbeat (hereinafter called “normalized ejection duration (diastolic time)”) may be used instead of the ejection duration (diastolic time). One cycle of the heartbeat decreases at a constant rate as the exercise load intensity increases, irrespective of the lactate threshold LT. On the contrary, the rate of change in the ejection duration differs across the lactate threshold LT as shown in FIG. 2 as described later. Therefore, the normalized ejection duration decreases in proportion to the rate of decrease in one cycle of the heartbeat as the exercise load intensity increases until the exercise load intensity reaches the lactate threshold LT. The rate of decrease in the normalized ejection duration significantly decreases after the exercise load intensity has reached the lactate threshold LT. On the contrary, the rate of change in the diastolic time differs across the lactate threshold LT as shown in FIG. 16 as described below. Therefore, the normalized diastolic time decreases as the exercise load intensity increases until the exercise load intensity reaches the lactate threshold LT. However, the rate of decrease in the normalized diastolic time is almost constant or increases to only a small extent irrespective of a decrease in one cycle of the heartbeat or pulse wave after the exercise load intensity has reached the lactate threshold LT. The subject can be notified that the exercise load intensity has reached the lactate threshold LT, or of the exercise load intensity and safety during exercise from the normalized ejection duration in each of the above aspects.
The notification section may notify the subject that the exercise load intensity is out of a safety exercise range by setting an ejection duration (diastolic time) exceeding the safe exercise range in a storage section in advance, and comparing the measured ejection duration (diastolic time) with the ejection duration (diastolic time) stored in the storage section.
Exercise equipment according to a further aspect of the present invention comprises the exercise load intensity evaluation device. The exercise equipment may output exercise menus of different degrees of exercise load intensity on a display section or the like, or change the exercise load intensity that is applied to the subject by using a load output section according to the exercise menu. For example, a belt velocity of a running/walking machine or pedal load of a pedal machine may be changed. The exercise load intensity and the cardiac ejection duration (diastolic time) may be measured in advance for each subject, and a safe and effective exercise menu may be set to the exercise equipment for each subject. A safe and effective exercise menu is set within a predetermined exercise load intensity range based on the lactate threshold calculated in advance for each subject from the correlation between the exercise load intensity and the ejection duration (diastolic time). The exercise load intensity range may be set near the lactate threshold for a person suffering from heart disease and a healthy person, for example. However, the exercise load intensity range may be set in a range temporarily exceeding the lactate threshold if the ejection duration decreases to only a small extent or further decreases. The exercise load intensity range may be set in a range exceeding the lactate threshold for an athlete, for example. The exercise load intensity range may be set as a range of the heart rate based on one cycle of the heartbeat output from the ejection duration (diastolic time) change detection section. An exercise menu suitable for a subject can be easily set if a storage medium which stores the exercise menu can be removed from the exercise equipment.